1. Field of the Invention
The present invention relates to a circuit for detecting a rotation angular velocity using an angular velocity sensor comprising an oscillator, and, more particularly, to a circuit for detecting a rotation angular velocity which can provide highly accurate measurements and is adapted to mass production.
2. Background Technology
Mechanical rotation-type gyroscopes have been conventionally used as an instrument for inertia navigation of airplanes and ships. Although these gyroscopes exhibit stable performances, they are large and expensive. It is difficult to fabricate them into small-type equipment.
The use of oscillator-type angular velocity sensors which detect Corioli's force from a detecting element on a vibrating object is being developed in recent years. In these sensors the mass of a gyroscope is vibrated at a specific frequency. When a rotation force is applied to the mass, a Corioli's force at the same frequency is created to the direction perpendicular to the vibration of the mass. The principle of the oscillator-type angular velocity sensor consists of measuring the mass vibration of this force for the determination of the angular velocity.
A circuit for detecting an angular velocity using an angular velocity sensor based on this principle is disclosed, for example, in Japanese Patent Application Laid-open (kokai) 172711/1991. The oscillator disclosed in this patent application is a coupling oscillator of a tuning-fork structure which comprises vibrator units, each consisting of a driving section and a detection section joined perpendicularly to each other, and coupling blocks connecting these vibrator units.
Conventionally, elastic-invariable metals, such as Elinvar, or PZT-type piezoelectric ceramics have been used as oscillators. In the case of oscillators using an elastic-invariable metal, electrodes are formed on the metal surface, a thin piezoelectric element is adhered to the electrodes, then electrodes are again formed on the piezoelectric element.
An oscillator circuit for vibrating an oscillator principally consists of an amplifier and a feedback circuit. The following formulas (1) and (2) apply to the vibration conditions of the circuit, EQU .vertline..alpha..vertline..multidot..vertline..beta..vertline.&gt;1(1) EQU .theta.1+.theta.2=360.degree. (2)
wherein .alpha. is the amplification factor of the amplifier, .theta.1 is the transmission rate of the feedback circuit, .beta. is the transmission rate of the feedback circuit, and .theta.2 is a phase lag. In order to satisfy the condition of the formula (2) conventional vibrator circuits for angular velocity circuits take a system of acquiring the phase lag of 360.degree. for one loop by a phase lag of 180.degree. at the amplifier, a phase lag of 90.degree. by a phase shift circuit comprising a combination of resistors and capacities, and another phase lag of 90.degree. by a resistor and the capacity of the piezoelectric element itself.
Conventional angular velocity detector circuits thus not only require a phase shift circuit, but also they must create a phase shift by a resistor and the capacity of the piezoelectric element itself. Because of this, the transmission rate .beta. of the feedback circuit and the phase lag .theta.2 may vary due to changes in the constant of the phase shift circuit which is caused by temperature changes, resulting in instability of the vibration. In addition, when a rotation force is applied, vibration produced by a Corioli's force in the oscillator is rendered unstable. This results in production of drift in the detector circuit output, leading to inaccuracy in the determination.
Furthermore, a decrease in the transmission rate .beta. in the feedback circuit caused by the resistance of the phase shift circuit requires an increased amplification factor .alpha. for the amplifier or provision of two or more amplifiers. Further, in order to stabilize the vibration by maintaining the transmission rate .beta. of the feedback circuit constant, a standard voltage generation circuit must be provided. This makes the detector circuit complicated.
The present invention has been achieved in order to solve these problems, and has an object of providing a circuit for detecting a rotation angular velocity, which is equipped with an oscillator circuit having a simple structure and capable of creating vibrations in a highly stable manner, and which provides high accuracy measurements and is adapted to mass production.